<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>This</title>
</head>
<body>
  <button id="J_btn">+</button>
  <button onclick="console.log(this)">-</button>
  <!-- this -> window 函数的作用域内部在行内里面默认指向的 window -->
  <button onclick="(function () {console.log(this)})()">test</button>
  <script src="./08-类.js"></script>
</body>
</html>